Method for mounting a length measuring device and corresponding length measuring device

ABSTRACT

A length measuring system that includes a length measuring device and at least one mounting element, which exerts an attractive force between a support and the length measuring device. One or more of the at least one mounting element are of such a size that a frictional force, which is a function of a total attractive force, assures on one hand an adhesion of the length measuring device to the support and, on another hand, also assures displaceablity of the length measuring device along the support during mounting.

[0001] The invention relates to a method for mounting a length measuringdevice, as well as the corresponding length measuring device itself

[0002] Such length measuring devices are used for example, as lineardistance measuring devices in automation technology or for testingdevices. Length measuring devices are also used on machine tools in verymany cases. It is necessary there to measure the length of the carriagein relation to the machine bed with great accuracy. For this purpose thehousing containing the scale graduation is fixedly screwed to themachine bed, for example, and the scanning unit of the length measuringdevice is connected with the movable carriage of the machine tool.

[0003] Often the length measuring devices are delivered as pre-assembledunits, which means that the scale and the scanning unit, which can bemoved in the measuring direction, are located together in one housing.Length measuring devices of this type are called closed, or encapsulatedlength measuring devices. But there are also so-called open lengthmeasuring devices, wherein the scanning unit and the scale are deliveredseparately.

[0004] It is necessary in both cases to align and fasten the housing, orthe scale, with the greatest possible parallelism with respect to themeasuring direction of the support, for example a machine tool.

[0005] In what follows, length measuring device means a closed, as wellas an open length measuring device. It is thus possible by means of theinvention to align and mount either only a scale, or a scale with ascanning unit, or a scale in a housing with a scanning unit containedtherein.

[0006] Because of the continued improvement of the measuring accuracy ofsuch length measuring devices, a correspondingly matched mountingaccuracy with respect to their alignment by means of customarytechniques becomes more and more elaborate. Measuring accuracies of ±5μm or less are quite customary with such length measuring devices.Therefore the time required for the appropriate exact adjustment of thedevices in the course of the mounting operations, for example on machinetools, is relatively great. Moreover, the mounting, or adjusting processitself is very difficult for a single assembler, particularly inconnection with length measuring devices of some length.

[0007] A method and a device intended for mounting a scale or a scalesupport on an appropriate machine element are described in DE 199 14 311A1. So that an undesired adhesive contact prior to the end of thealignment of the scale is prevented, spacers are proposed in thisdocument, so that the scale can be definitely adjusted before it comesinto contact with its support.

[0008] In DE 37 15 908 C2, a flexible scale with magnetic holders orsuction cups is fastened on a body to be measured. This fastening whichcan be released relatively easily is also used during the measuringprocess itself. The disadvantage of this invention is that a permanentprecise fixation of the scale is not possible in any way.

[0009] The same applies to published patent application EP 0 922 927 A2,wherein a magnetic fixation on the body to be measured is provided forthe measuring process. There, too, the length measuring scale is notpermanently brought into contact with the measuring body, and relativelylow demands are made on the measuring accuracy.

[0010] The object of the invention is based on disclosing a method formounting a length measuring device, by means of which a simple andaccurate alignment of the length measuring device, or of the scale, onits support becomes possible. It is moreover intended to disclose alength measuring device which is distinguished by easy manipulation anduniversal employment.

[0011] This object is attained by means of a method in accordance withclaim 1 and a device in accordance with claim 10.

[0012] Advantageous embodiments are disclosed in the dependent claims.

[0013] So-called mounting elements, which exert an attractive forcebetween the length measuring device and the support, for example themachine bed of a machine tool, are used for making mounting easier. Ifthe said support surface is perpendicularly arranged, an adhesivefriction force results, which corresponds to the product of attractiveforce and the corresponding coefficient of friction. For thedetermination of the sum of the normal forces in connection with obliqueor horizontal surfaces it is necessary to take into account, besides thetotal attractive force, also the weight with positive or negative signsin accordance with the respective inclination of the support. Inaccordance with the invention, the sum of the attractive forces of allmounted elements is of such a size that, on the one hand, the lengthmeasuring device adheres to the surface of the support in the installedposition but, on the other hand, the displacement of the device foradjusting purposes is still possible. This means that the lengthmeasuring device can possibly be manually displaced on the surface ofthe support and aligned.

[0014] Thereafter it is absolutely necessary for the permanent use ofthe entire system that the length measuring device be fixedly connectedwith the support, for example by screw connections. In this state thedevice cannot be inadvertently, or without being damaged, moved out ofadjustment. Alternatively to this it is also possible to provide apermanent adhesive connection, as long as the adhesive permits a lineardisplacement of the length measuring device in the adjusting phase—inwhich the length measuring device and the support adhere to each other.In this connection adhesives on the basis of epoxy resins, for example,are advantageous, which have a setting time which is greater than thetime required for the exact alignment. The use of adhesives, whosesetting phase can be specifically initiated from the outside, ispractical. Adhesives can be used in this connection, whose setting isinitiated, or significantly accelerated, by heat, UV radiation, moistureor other activators, for example. The length measuring device can bestructurally adapted to these adhesives in an advantageous manner. Forexample, relatively large recesses or bezels can be provided at the endpieces, so that an increased adhesive surface is provided to the meanswhich initiate setting.

[0015] At the end of the setting time, a non-displaceable connectionmust also be assumed. The adhesive can be applied in spots over theentire contact surface, or over a considerable partial surface. In thiscase the level application of the adhesive can the be considered as alineup of many adhesive spots.

[0016] Magnets are particularly suited as mounting elements. The use ofpermanent magnets is advantageous since, in comparison withelectromagnets, it is possible here to dispense with the electricalauxiliary energy. If an embodiment variation is used which does notprovide the removal of the mounting magnets at the end of mounting, theelectromagnetic solution can also be advantageous, because in this caseno magnetic forces are present during the operation of the lengthmeasuring device which—for example in connection with machinetools—could trigger the undesired attraction of metal chips. For thesame reason an arrangement of the permanent magnets is provided in anembodiment variation of the invention, wherein the magnets arecompletely surrounded by a steel housing of the length measuring devicewith the exception of their side facing the support. The size of themagnetic field toward the outside is minimized by the magnetic shortcircuit between the support and the magnets.

[0017] The use of suction cups as mounting elements for the temporaryfastening of the length measuring device on the support is recited as afurther embodiment of the invention. These suction cups can becomeeffective either by merely pressing the suction cup on, or alsoactively, for example by means of appropriate clamping devices or aidedby compressed air.

[0018] With shorter length measuring devices the mounting elements arepreferably located in the two end areas of the length measuring devices.However, particularly in connection with long length measuring devices,it can be advantageous to arrange several mounting elements over theentire length of the length measuring device, spaced apart in themeasuring direction.

[0019] Exemplary embodiments of the invention will be explained ingreater detail by means of the drawings.

[0020] Shown are in:

[0021]FIGS. 1a to 1 c, schematically the respective process steps formounting the length measuring device,

[0022]FIGS. 2A, 2b, a cross section and a partial view from above on anend element of a length measuring device with permanent magnet units,

[0023]FIGS. 3a, 3 b, a cross section and a partial view from above on anend element of a length measuring device with removable permanent magnetunits,

[0024]FIGS. 4a, 4 b, a cross section and a partial view from above on anend element of a length measuring device with magnets in the machinebed,

[0025]FIGS. 5a, 5 b, a cross section and a partial view from above on anend element of a length measuring device with a permanent magnet stuckon it,

[0026]FIGS. 6a, 6 b, a cross section and a partial view from above on anend element of a length measuring device with an inserted magnetic pin,

[0027]FIGS. 7a, 7 b, a cross section and a partial view from above on anend element of a length measuring device with suction cups,

[0028]FIGS. 8a, 8 b, a cross section and a partial view from above on anend element of a length measuring device with an adhesive connection.

[0029] In the drawing figures, elements which are part of a component orhave the same function are combined by means of identical first numbersof the reference numeral.

[0030]FIGS. 1a to 1 c are essentially intended to explain the course ofthe method. The length measuring device 1, consisting of the scanningunit 1.1, the end elements 1.2 and the encapsulated linear scale 1.3, isto be mounted on the support, in this case on the machine bed 2 of amachine tool. It is necessary in the course of this to assure that thealignment Y of the length measuring device 1 is as parallel as possibleto the desired direction X. The desired direction X corresponds to thedirection of guidance of the movable carriage 3 of the machine tool.

[0031]FIG. 1a represents the position of the length measuring device 1during the first mounting step. To make the situation clear, thedeviation of the actual alignment Y from the desired direction X isexaggerated. In this first mounting step the length measuring device 1is put into frictional contact on the perpendicular flat surfaces of themachine bed 2 without use of exact measuring means and in a firstapproximation parallel with respect to X. Following this mounting phase,the length measuring device 1 adheres to the machine bed 2 withoutmanual support. If the play between the exterior thread of the screws 4and the interior diameter of the bore 1.5 is of sufficient size, it isalready possible to loosely thread the screws 4 through the bores 1.5during the first mounting step. Means for achieving the requiredadhesive friction will be described later by means of FIGS. 2a to 8 b.

[0032] In the second mounting step, represented in FIG. 1b, it is theneasily possible to perform the exact alignment of the length measuringdevice 1 with the required measuring means. Because the length measuringdevice 1 adheres to the machine bed 2 without any aid from theassembler, but is nevertheless comparatively easily manuallydisplaceable, a quick and very exact adjustment is possible. Noundesired mechanical loads on the measuring device 1 occur in the courseof the alignment, because an improper mounting, for example an alignmentof the already screw-connected length measuring device 1 by beating onit, can be prevented with this method. It is of course possible toprovide a lubricant or sliding additive between the length measuringdevice 1 and the machine bed 2 in order to ease the displaceability, orto avoid so-called slip-stick effects. The bores 1.5 are used forreceiving screws 4 for the final fastening after the exact alignment ofthe length measuring device 1 on the machine bed 2. It is also necessaryin the course of displacing the length measuring device 1 to assure thatthe bores 1.5 in the length measuring device 1 match the correspondingbores with an interior thread in the machine bed 2. As a rule, the bores1.5 have a slightly larger interior diameter than the diameter of theexterior thread of the associated screws 4. In this way sufficient playis provided for making the alignment possible without it being necessaryto perform drilling during the mounting process.

[0033] The last mounting step is represented in FIG. 1c. After theadjustment is finished, for example with a deviation of the actualdirection Y from the desired direction X of less than 0.1 degrees ofangle, the length measuring device 1 is solidly and immovably fixed onthe machine bed by means of screws 4. In this state the scanning unit1.1 can be displaced almost parallel in relation to the desireddirection X, i.e. the movement direction of the carriage 3.

[0034] An end element 1.2 of a housing of the length measuring device 1is represented in each of FIGS. 2 to 8. Like the rest of the housing,these end elements 1.2 are often made of aluminum, i.e. of anon-ferromagnetic material.

[0035]FIGS. 2a and 2 b show an arrangement in which the mountingelements are permanent magnets 5.11. In this case the machine bed 2 ismade of a ferromagnetic material, for example of steel. If required, thepermanent magnets 5.11 can be backed by a rear closure plate 5.12 forincreasing the attractive force, in particular if there is an aluminumhousing. For example, the magnets can be glued to the rear closure plate5.12, or the attractive force of the magnets on the rear closure plate5.12 can be used for fixation. In this case the rear closure plate 5.12can be inseparably connected with the housing by gluing.

[0036] Basically, it is advantageous for all exemplary embodiments thatthe mounting elements are designed in such a way that they do not becomeseparated, or fall of, from the length measuring device 1 in the courseof the mounting work.

[0037] If magnets are used as mounting elements, they are preferablyinserted into the housing of the length measuring device 1 in such a waythat their surface is flush with the surface of the length measuringdevice 1, or is slightly set back. It is achieved by means of thisconstruction that the corresponding surfaces of the length measuringdevice 1 and of the machine bed 2 are in contact during the entiremounting phase. So that the length measuring device 1 can be mounted bymeans of the method of the invention on both possible attachmentsurfaces 1.7, the mounting elements in the exemplary embodiments inaccordance with FIGS. 2 to 4, as well as 7 and 8, are arranged, or canbe arranged, symmetrical, in particular point-symmetrical, with respectto the center of the cross section of the length measuring device.

[0038]FIGS. 3a and 3 b show a variation, wherein the mounting element isembodied as a removable permanent magnet unit 5.1 with a correspondingrear closure plate 5.12. So that the permanent magnets 5.11 and the rearclosure plate 5.12 are sufficiently secure against falling out, undercutrecesses 1.4 are provided here in the end elements 1.2 of the lengthmeasuring element 1, which are used as guides for the rear closure plate5.12. To ease the pulling out of the permanent magnet unit 5.1, the rearclosure plate 5.12 is appropriately bent at one end (in the partial viewfrom above in FIG. 3b, the rear closure plate 5.12 projects out of thedrawing plane at one end). The removed permanent magnet unit 5.1 can beused again with another length measuring device 1 to be mounted.

[0039]FIGS. 4a and 4 b show an embodiment variation, wherein the machinebed 2 consists of a non-ferromagnetic material, such as granite orpolymer concrete, for example. A permanent magnet 2.2 can be insertedinto the machine bed 2 here, which then interacts with a ferromagneticinsert 5.3 of the length measuring device. It is of course possible toembody the inserts in the length measuring device 1 in the form ofpermanent magnets, similar to FIGS. 2 and 3, if correspondingmagnetically attractive reaction elements, for example strips of steelplate, are then provided in the non-ferromagnetic machine bed 2.

[0040] Alternatively to the embodiments represented so far, anarrangement is represented in FIGS. 5a and 5 b, in which ahorseshoe-shaped permanent magnet 5.11 extends around the respective endelement 1.2. A supporting frictional connection is created by themagnetic attractive force between the machine bed 2 and the permanentmagnet 5.11. This frictional connection has a support ability which issufficiently strong so that the frictional connection is not releasedeven during displacement movement in the course of the adjustingprocess. The permanent magnets 5.11 can be pulled off in a simple mannerafter the mounting process.

[0041] A variation is represented in FIGS. 6a and 6 b, wherein amagnetic pin 5.2 can be inserted into an auxiliary bore 1.6 in the endelement 1.2 of the length measuring device 1. This variation isdistinguished by its simple construction. In contrast to the variationin FIG. 5, an interlocking force transfer between the permanent magnet5.1 and the end element 1.2 is provided here. Here, too, the lengthmeasuring device 1 in accordance with the method of the invention can befastened on both possible attachment surfaces 1.7 of the machine bed 2.The magnetic pin 5.2 should be designed in such a way that it cannotfall out in the course of the mounting operations. The embodiment shown,wherein the pin 5.2 is secured by means of an appropriately tight fit,is particularly advantageous from the viewpoint of production costs.

[0042] Alternatively to this it is also possible for axial securing toprovide a plastic element, which is pushed against the wall of theauxiliary bore 1.6 in the course of introducing the pin 5.2, or anappropriate screw thread.

[0043] An embodiment variation is represented in FIGS. 7a and 7 b,wherein the adhesive friction is caused by suction cups 5.4 made of apolymer material. Here, too, the application of a lubricant or a slidingadditive can be particularly advantageous, for one, to increase thedisplaceability, and furthermore to prevent the penetration of air intothe underpressure area of the suction cup 5.4.

[0044] Finally, an exemplary embodiment is represented in FIGS. 8a and 8b, wherein the adhesive connection is produced by means of a glueconnection 5.5. In this case the glue connection 5.5 can be used as amounting element, as well as a permanent fastening means for the lengthmeasuring device 1. In this case the length measuring element 1 isprovided with bezels 1.8 of comparatively large size. An adhesive isapplied to the attachment surface 1.7, which is distinguished in thatits setting process can be triggered by UV radiation. As soon as thelength measuring device 1 has been adjusted with sufficient accuracy,the visible glue joints are radiated with UV radiation by the assembler.The polymerization process of the adhesive is started in this way.Setting in the areas of the glue connection 5.5 where no UV radiationpenetrates is made possible by an anaerobic secondary system of theglue. Since the glue connection 5.5 shows great strength in the setstate, the use of the screws 4 can be dispensed with.

1. A method for mounting a length measuring device (1) on a support (2),wherein in a first mounting step the length measuring device (1) isplaced into frictionally adhesive contact with the support surface,wherein at least one mounting element (5.1, 5.2, 5.3, 5.4, 5.5) exertsan attractive force between the support (2) and the length measuringdevice (1), and this attractive force is of such a size that thecorresponding frictional force assures a displaceability of the lengthmeasuring device (1), in a second mounting step the position anddirection of the length measuring device (1) is adjusted, so that itsorientation, in the sense of the result of the length measurement, has aa tolerably small deviation from the desired direction, in a thirdmounting step the length measuring device is connected with its support(2) so that it cannot be displaced.
 2. The method in accordance withclaim 1, characterized in that the length measuring device (1) is analready pre-assembled unit consisting at least of one linear scale (1.3)and at least one scanning unit (1.1).
 3. The method in accordance withclaim 1, characterized in that at least two spaced apart mountingelements (5.1, 5.2, 5.3, 5.4, 5.5) are arranged on the length measuringdevice (1), by means of which the length measuring device (1) isconnected with its support.
 4. The method in accordance with one ofclaims 1 to 3, characterized in that at least one mounting element (5.1,5.2, and 5.3) exerts a magnetic attractive force between the support (2)and the length measuring device (1).
 5. The method in accordance withone of claims 1 to 3, characterized in that at least one mountingelement (5.4) exerts an attractive force, which is caused byunderpressure, between the support (2) and the length measuring device(1).
 6. The method in accordance with claim 1, characterized in that inthe third mounting step the length measuring device (1) is connected ina non-displaceable manner with its support (2) with the aid of screwand/or rivet connections in at least two points.
 7. The method inaccordance with claim 1, characterized in that in the third mountingstep the length measuring device (1) is connected in a non-displaceablemanner with its support (2) by means of an adhesive connection (5.5) inat least two points.
 8. The method in accordance with claim 7,characterized in that in the second mounting step the adhesiveconnection (5.5) is in a state which permits a displacement of thelength measuring device (1) in relation to the support (2), andthereafter leads to a solid connection between the length measuringdevice (1) and the support (2).
 9. The method in accordance with claim1, characterized in that all, or only a part, of the mounting elements(5.1, 5.2, 5.3, 5.4, 5.5) are removed in a fourth mounting step.
 10. Alength measuring device (1), having at least one mounting element (5.1,5.2, 5.3, 5.4, 5.5), which exerts an attractive force between a support(2) and the length measuring device (1), wherein the mounting element orthe mounting elements (5.1, 5.2, 5.3, 5.4, 5.5) are of such a size thatthe frictional force, which is a function of the total attractive force,assures on the one hand the adhesion of the length measuring device (1)to the support (2) and, on the other hand, also assures thedisplaceablity of the length measuring device (1) along the supportsurface during mounting.
 11. The length measuring device in accordancewith claim 10, characterized in that the length measuring device (1) isan already pre-assembled unit consisting at least of one linear scale(1.3) and at least one scanning unit (1.1).
 12. The length measuringdevice in accordance with claim 10, characterized in that the mountingelements (5.1, 5.2, 5.3, 5.4, 5.5) are or can be arranged in such a waythat the length measuring device (1) can be alternatively brought intoan adhesive frictional contact with a support (2) on at least twoattachment surfaces (1.7).
 13. The length measuring device in accordancewith one of claims 10 to 12, characterized in that at least two mountingelements (5.1, 5.2, 5.3, 5.4, 5.5) are arranged on the length measuringdevice (1).
 14. The length measuring device in accordance with claim 13,characterized in that the mounting elements (5.1, 5.2, 5.3, 5.4, 5.5)are arranged on the two end sections (1.2) of the length measuringdevice (1).
 15. The length measuring device in accordance with one ofclaims 10 to 14, characterized in that at least one mounting element(5.1, 5.2, 5.3) exerts a magnetic attractive force between the support(2) and the length measuring device (1).
 16. The length measuring devicein accordance with claim 15, characterized in that at least onepermanent magnet (5.11) is arranged for generating a magnetic attractiveforce between the support (2) and the length measuring device (1). 17.The length measuring device in accordance with claim 15, characterizedin that at least one switchable magnet, in particular an electromagnet,is arranged for generating a magnetic attractive force between thesupport (2) and the length measuring device (1).
 18. The lengthmeasuring device in accordance with claim 15, characterized in that onthe surfaces facing away from the support (2), the magnets (5.11) areprovided with rear closure plates (5.12).
 19. The length measuringdevice in accordance with claim 10, characterized in that the magnets(5.11) are fastened in the length measuring device (1) with the aid ofseveral undercut recesses (1.4), in particular one or several dovetailedrecesses.
 20. The length measuring device in accordance with claim 15,characterized in that the length measuring device (1) has at least oneauxiliary bore (1.6) extending into it, into which cylindrical magnets(5.2) can be inserted.
 21. The length measuring device in accordancewith claim 15, characterized in that at least one ferromagnetic reactionelement (5.3) is attached to the length measuring device (1), which isattracted by one or several magnets (2.2) housed in the support (2). 22.The length measuring device in accordance with one of claims 10 to 14,characterized in that at least one mounting element (5.4) creates anattractive force, which is caused by underpressure, between the support(2) and the length measuring device (1).
 23. The length measuring devicein accordance with claim 10, characterized in that the length measuringdevice (1) is designed in such a way that all, or only a part, of themounting elements (5.1, 5.2, 5.3, 5.4, 5.5) can be removed aftermounting has been completed.